Table 12-6 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM mode.
Table 12-6. Compare Output Mode, Fast PWM Mode(1)
COM0B1
COM0B0
Description
0
0
1
1
0
1
0
1
Normal port operation, OC0B disconnected.
Reserved
Clear OC0B on compare match, set OC0B at TOP
Set OC0B on compare match, clear OC0B at TOP
Note:
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 12.6.3 “Fast PWM Mode” on page 83 for more details.
Table 12-7 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 12-7. Compare Output Mode, Phase Correct PWM Mode(1)
COM0B1
COM0B0
Description
0
0
0
1
Normal port operation, OC0B disconnected.
Reserved
Clear OC0B on compare match when up-counting. Set OC0B on compare match
when down-counting.
1
1
0
1
Set OC0B on compare match when up-counting. Clear OC0B on compare match
when down-counting.
Note:
1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the compare match is
ignored, but the set or clear is done at TOP. See Section 12.6.4 “Phase Correct PWM Mode” on page 84 for
more details.
• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the ATmega16/32/64/M1/C1 and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B register, these bits control the counting sequence of the counter, the
source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 12-8. Modes of
operation supported by the Timer/Counter unit are: Normal mode (counter), clear timer on compare match (CTC) mode, and
two types of pulse width modulation (PWM) modes (see Section 12.6 “Modes of Operation” on page 81).
Table 12-8. Waveform Generation Mode Bit Description
Timer/Counter
Mode of Operation
Update of
OCRx at
TOV Flag
Set on(1)(2)
Mode
WGM02
WGM01
WGM00
TOP
0xFF
0xFF
OCRA
0xFF
–
0
1
2
3
4
5
6
7
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Normal
Immediate
TOP
MAX
BOTTOM
MAX
PWM, phase correct
CTC
Immediate
TOP
Fast PWM
MAX
Reserved
–
–
PWM, phase correct
Reserved
OCRA
–
TOP
BOTTOM
–
–
Fast PWM
OCRA
TOP
TOP
Notes: 1. MAX
= 0xFF
2. BOTTOM = 0x00
88
ATmega16/32/64/M1/C1 [DATASHEET]
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
